1. Field of the Invention
The present invention relates to a photographing lens having a memory means in which lens data peculiar to the photographing lens is stored.
2. Description of Related Art
A photographing lens (interchangeable lens) in a recent single lens reflex camera having an automatic focusing device is usually provided with a memory (e.g., ROM) in which lens data peculiar to the photographing lens is stored. The camera body is provided with a control means which communicates with the memory to read the lens data stored therein and performs predetermined arithmetic operations (exposure calculation and AF calculation) for calculating exposure factors (diaphragm value, shutter speed, etc.), the amount of defocus, and a displacement of a focusing lens to be moved, etc., in accordance with the lens data, based on predetermined algorithm and formulae.
The lens data includes, for example, an apex value Avmin at an open aperture (open F-number), an apex value Avmax at a minimum aperture (minimum aperture F-number), focal length data f, and object distance data, etc.
A part of the lens data varies in accordance with the photographing conditions. Namely, the lens data partly varies in accordance with the object distance in the case of a single focus lens, and varies in accordance with the focal length in the case of a zoom lens, respectively.
Accordingly, in the case of a single focus lens, the object distance is divided into a plurality of object distance zones, so that the lens data corresponding to the object distance zones are, stored in predetermined memory areas of the ROM. In the case of a zoom lens, the focal length is divided into a plurality of focal length zones, so that the lens data corresponding to the focal length zones are stored in predetermined memory areas of the ROM. Namely, the lens data is stored for every photographing condition in a page-address system.
The object distance and the focal length are detected by an object distance detecting device and a focal length detecting device, respectively, so that the lens data stored in the pages corresponding to the data thus detected is outputted to the camera body as renewed lens data.
In the course of manufacturing a photographing lens having a memory, as mentioned above, whether or not the correct lens data is stored at a predetermined address corresponding to the detected object distance or focal length must be checked.
However, upon the checking, it is necessary to actually carry out the zooming operation or the focus adjustment in order to read the lens data corresponding to the detected object distance or the detected focal length, which is troublesome. Furthermore, if the necessary lens data is not obtained, a photographer can not determine whether the problem is caused by an error of the lens ROM or a trouble with the detecting devices, etc.